Mg-Al anionic clay having 3R2 stacking

Details Mg-Al anionic clay having 3R2 stacking Mg-Al anionic clay having 3R2 stacking

2000-08-11

2002-10-22

Silverman, Stanley S. (Department: 1754)

Chemistry of inorganic compounds

Modifying or removing component of normally gaseous mixture

Nitrogen or nitrogenous component

C423S244010, C423S244090, C423S593100, C423S600000, C423S625000, C423S635000, C502S080000, C502S084000, C502S414000, C252S363500, C252S397000

Reexamination Certificate

active

06468488

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention pertains to a new polytype of Mg—Al anionic clay.
2. Description of the Prior Art
Anionic clays have a crystal structure which consists of positively charged layers built up of specific combinations of metal hydroxides between which there are anions and water molecules. Hydrotalcite is an example of a naturally occurring anionic clay, in which carbonate is the predominant anion present. Meixnerite is an anionic clay wherein OH
−
is the predominant anion present.
In hydrotalcite-like anionic clays the brucite-like main layers are built up of octahedra alternating with interlayers in which water molecules and anions, more particularly carbonate ions, are distributed. The interlayers contain anions such as NO
3
−
, OH, Cl
−
, Br
−
, I
−
, SO
4
2−
, SiO
3
2−
, CrO
4
2−
, BO
3
2−
, MnO
4
−
, HGaO
3
2−
, HVO
4
2−
, ClO
4
−
, BO
3
2−
, pillaring anions such as V
10
O
28
−6
and MO
7
O
24
6−
, monocarboxylates such as acetate, dicarboxylates such as oxalate, and alkyl sulfonates such as laurylsulfonate.
Anionic clays have a layered structure corresponding to the general formula
[Mg
m
2+
Al
n
3+
(OH)
2m+2n
.]X
n/z
z−
.bH
2
O
Wherein m and n have a value such that m
=1 to 10, preferably 1 to 6, and b has a value in the range of from 0 to 10, generally a value of 2 to 6 and often a value of about 4. X may be CO
3
2−
, OH
−
or any other anion normally present in the interlayers of anionic clays. It is more preferred that m
should have a value of 2 to 4, more particularly a value close to 3.
It should be noted that a variety of terms is used to describe the material which is referred to in this patent as an anionic clay. Hydrotalcite-like and layered double hydroxide are interchangeably used by those skilled in the art. In this patent application we refer to the materials as anionic clays, comprising within that term hydrotalcite-like and layered double hydroxide materials.
The preparation of anionic clays has been described in many prior art publications.
Two major reviews of anionic clay chemistry were published in which the synthesis methods available for anionic clay synthesis have been summarized, F. Cavani et al “Hydrotalcite-type anionic clays: Preparation, Properties and Applications,”
Catalysis Today”,
11 (1991) Elsevier Science Publishers B. V. Amsterdam. J P Besse and others “
Anionic clays: trends in pillaring chemistry, its synthesis and microporous solids”
(1992), 2, 108, editors: M. I. Occelli, H. E. Robson, Van Nostrand Reinhold, N.Y.
In these reviews two structurally different forms of anionic clays are described: the 3R
1
(three-layer repeat) and the 2H
1
(two-layer repeat) corresponding to hydrotalcite and manassite, respectively. The Mg—Al anionic clays prepared by conventional preparation methods such as co-precipitation, optionally followed by hydrothermal treatment or aging to increase the crystallite size, have a 3R
1
stacking. Also naturally occurring hydrotalcite has the 3R
1
stacking.
In the publications in
Clay and Clay Minerals
, Vol 41, No.5, pages 551-557 and pages 558-564 of Bookin and Drits, it is stated that 3R
2
polytypes have been observed in nature, however, only in sulfate Mg—Al anionic clays.
For further work on anionic clays, reference is given to the following articles:
Helv. Chim. Acta,
25, 106-137 and 555-569 (1942)
J. Am. Ceram. Soc.,
42, no. 3, 121 (1959)
Chemistry Letters
(Japan), 843 (1973)
Clays and Clay Minerals,
23, 369 (197)
Clays and Clay Minerals,
28, 50 (1980)
Clays and Clay Minerals,
34, 507 (1996)
Materials Chemistry and Physics,
14, 569 (1986).
In addition there is an extensive amount of patent literature on the use of anionic clays and processes for their preparation.
The prior art described below describes the preparation of anionic clays by the co-precipitation method:
European Patent Application 0 536 879 describes a method for introducing pH-dependent anions into the clay. The clay is prepared by the addition of a solution of Al(NO
3
)
3
and Mg(NO
3
)
2
to a basic solution containing borate anions. The product is then filtered, washed repeatedly with water, and dried overnight. Additionally mixtures of Zn/Mg are used.
In U.S. Pat. No. 3,796,792 by Miyata et al. entitled “Composite Metal Hydroxides” a range of materials is prepared into which an extensive range of cations is incorporated, including Sc, La, Th, In, etc. In the examples given solutions of the divalent and trivalent cations are prepared and mixed with base to cause co-precipitation. The resulting products are filtered, washed with water, and dried at 80° C. Example 1 refers to Mg and Sb and Example 3 to Mg and Bi. Other examples are given, and in each case soluble salts are used to make solutions prior to precipitation of the anionic clay at high pH.
In U.S. Pat. No. 3,879,523 by Miyata entitled “Composite Metal Hydroxides” also a large number of preparation examples are outlined. The underlying chemistry, however, is again based on the co-precipitation of soluble salts followed by washing and drying. It is important to emphasize that washing is a necessary part of such preparations, because to create a basic environment for co-precipitation of the metal ions a basic solution is needed and this is provided by NaOH/Na
2
CO
3
solutions. Residual sodium, for example, can have a significant deleterious effect on the subsequent performance of the product as a catalyst or oxide support.
In U.S. Pat. No. 3,879,525 (Miyata) very similar procedures are again described.
In U.S. Pat. No. 4,351,814 to Miyata et al. a method for making fibrous hydrotalcites is described. Such materials differ in structure from the normal plate-like morphology. The synthesis again involves soluble salts. For example, an aqueous solution of a mixture of MgCl
2
and CaCl
2
is prepared and suitably aged. From this a needle-like product Mg
2
(OH)
3
Cl.4H
2
O precipitates. A separate solution of sodium aluminate is then reacted in an autoclave with the solid Mg
2
(OH)
3
Cl.4H
2
O and the product is again filtered, washed with water, and dried.
In U.S. Pat. No. 4,458,026 to Reichle, in which heat-treated anionic clays are described as catalysts for aldol condensation reactions, again use is made of magnesium and aluminum nitrate salt solutions. Such solutions being added to a second solution of NaOH and Na
2
CO
3
. After precipitation the slurry is filtered and washed twice with distilled water before drying at 125° C.
In U.S. Pat. No. 4,656,156 to Misra the preparation of a novel absorbent based on mixing activated alumina and hydrotalcite is described. The hydrotalcite is made by reacting activated MgO (prepared by activating a magnesium compound such as magnesium carbonate or magnesium hydroxide) with aqueous solutions containing aluminate, carbonate and hydroxyl ions. As an example the solution is made from NaOH, Na
2
CO
3
and Al
2
O
3
. In particular, the synthesis involves the use of industrial Bayer liquor as the source of Al. The resulting products are washed and filtered before drying at 105° C.
In U.S. Pat. No. 4,904,457 to Misra a method is described for producing hydrotalcites in high yield by reacting activated magnesia with an aqueous solution containing aluminate, carbonate, and hydroxyl ions.
The methodology is repeated in U.S. Pat. No. 4,656,156.
In U.S. Pat. No. 5,507,980 to Kelkar et at al. a process is described for making novel catalysts, catalyst supports, and absorbers comprising synthetic hydrotalcite-like binders. The synthesis of the typical sheet hydrotalcite involves reacting pseudo-boehmite to which acetic acid has been added to peptize the pseudo-boehmite. This is then mixed with magnesia.
In U.S. Pat. No. 6,539,861 a process is disclosed for preparing a catalysts for synthesis gas production based on hydrotalcites. The method of preparation is again based, on the co-precipitation of soluble salts by mixing with base, for example, by t

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